The goal of this study is to identify proteins and mechanisms that regulate filamentous growth and pathogenesis in the oral microbe Candida albicans, the primary pathogen causing oral candidiasis. One of the major regulators of filamentous growth in Candida and other fungal species are signal transduction pathways. The signaling pathway on which the proposal is focused is the Cek1 MAPK pathway, which plays a critical role in hyphal invasive growth. We will investigate the cell-surface signaling mucin Msb2 that regulates this pathway to determine how Msb2 is activated in C. albicans, what proteins regulate Msb2 function, what Msb2 is sensing at the cell surface, and what roles it might play in regulating filamentous growth, biofilm formation, and immune system interactions. We will test quorum-sensing molecules and expression of Sap proteases for Msb2-dependent Cek1 activation. We will also test whether the extracellular glycodomain of Msb2, which we show is released from cells, plays a role in biofilm/mat formation and cell-surface architecture. Signaling mucins such as Msb2 are an evolutionary conserved class of cell-surface glycoproteins that have only recently been studied in microbial species. Signaling pathways sense changes in the extracellular environment and relay those changes to the inside of the cell. Because signaling pathways exert global control over cellular behaviors, they represent attractive targets to shut down or inhibit cellular differentiation programs or target genes. Given the serious threat of this fungal pathogen to human health, and given that current strategies to treat Candidal infections are in many cases ineffectual, our long-term goal is a deeper understanding of the pathogenic response in this microbe in order to identify a new class of drug targets.